The invention relates to a gimbal control mechanism to resist gimbal rotation about the major axis when the gyroscope approaches gimbal lock position and thereafter orients the gimbals and the spin axis of the gyroscope preparatory to the erecting or leveling as a condition precedent to reapplying power to the gyroscope rotor.
Gyroscopes are used to indicate angular rotation about the three principal control axes and are referred to as vertical gyroscopes and directional gyroscopes. Vertical gyroscope, whose starting sequence first requires erecting the gyro rotor spin axis, indicates pitch and roll, while the directional gyroscope, whose starting sequence first requires leveling the gyro rotor spin axis, indicates aximuth or yaw. The gyroscopes are completely free to rotate in the gimbal supports. Such gyroscopes have, however, a distinct disadvantage i.e., gimbal lock. Gimbal lock being defined as that condition which exists when the inner gimbal of the gyroscope rotates through such an angle about the inner gimbal axis that the spin axis of the rotor and the outer gimbal axis mounted in the frame supports are aligned. To avoid gimbal lock, a fixed stop means, situated to operate between the inner and the outer gimbal, was developed. Consequently, as the fixed stop means is engaged during a maneuver tending to swing the gyroscope to or through the gimbal lock position, torques are developed which quickly rotate the outer gimbal around, thereby circumventing gimbal lock and leaving the gyroscope free to rotate relative to the inner gimbal without further interference from the stop means. However, violent or rapid movements of the frame of the gyroscope cause accelerated angular deviations between the inner gimbal, and outer gimbal, so that the inner gimbal strikes the fixed stop with a highly intensive force. When this occurs, a very large torque is developed, causing the outer gimbal to tumble or upset.
The phenomenon of violent and rapid movement of the frame is particularly apparent when the gyro is of the type used for torpedoes, and the torpedo after its run and, with all power off, is coasting to the surface during the recovery cycle. As the result of power off, the steering vanes of the torpedo are skewed in a particular manner, causing the torpedo to pitch up and rotate with a high angular velocity.
The gyro, if equipped with a fixed stop means to prevent gimbal lock and gimbal tumbling, will, as a consequence, undergo accelerated precessional effects. These precessional effects will become particularly more rapid and cause breakage and damage to the gyro gimbals and bearings as the gyro rotor loses angular momentum during coast-down time.
The gyro resistance to external forces is dependent upon the angular momentum of the gyro rotor and this resistance is known as rigidity or stability. As the result of loss of rigidity or stability along with the aforementioned combination of external force, the gyro will undergo a sequence of violent and damaging rotations and tumbling, with resulting breakage of gyro gimbals and destruction of gimbal bearings.